Fires inside specific upload-type views in the legacy (pre-3.5.0) media popup based on the current tab.
The dynamic portion of the hook name,
$type, refers to the specific media upload type. Possible values include ‘image’, ‘audio’, ‘video’, ‘file’, etc.
The hook only fires if the current
$tab is ‘type’ (From Computer), ‘type_url’ (From URL), or, if the tab does not exist (i.e., has not been registered via the ‘media_upload_tabs’ filter.